This application is submitted in response to RFA-HL-10-027. As indicated in the RFA announcement, The goals of this RFA are to elucidate, in animal models, the cellular and molecular mechanisms that underlie large artery stiffening and determine the role of arterial stiffening in the etiology of hypertension. Klotho is a recently-discovered anti-aging gene. Genetic mutation of klotho results in multiple premature aging phenotypes while overexpression of klotho extends lifespan. Cardiovascular disease is associated with aging. In humans, the prevalence of arterial stiffening and hypertension increases with age while the level of circulating klotho decreases with age. It is not known, however, if klotho is involved in the maintenance of normal arterial compliance. Whether klotho gene deficiency causes arterial stiffening has never been determined. Chronic kidney disorders are associated with arterial stiffening. Our new preliminary studies showed that conditional kidney- specific knockout of klotho gene (KL-KO) caused arterial stiffening and systolic hypertension. The objective of the proposed research is to determine the role of kidney-derived klotho in the maintenance of arterial compliance and the molecular mechanisms that mediate klotho deficiency-induced arterial stiffening and its relationship to the development of hypertension. This objective will be achieved by pursuing three coherent specific aims using a combination of experimental approaches including conditional kidney-specific gene knockout, in vivo gene delivery, and real-time monitoring of blood pressure (telemetry). (1) Determine the contribution of impaired endothelial function (down-regulation of eNOS) and oxidative stress (up-regulation of NADPH oxidase p47phox) to the KL-KO-induced arterial stiffening and systolic hypertension. (2) Determine the role of the up-regulation of MMP-9, TGF-21, and runt-related transcription factor-2 (RUNX-2) in SMCs and their relationship in KL-KO- induced elastin degradation, osteoblastic transition, calcification (elastocalcinosis), and arterial stiffening and systolic hypertension. (3) Determine the effects of therapeutic prevention of a decline in the circulating klotho on the development of arterial stiffening and systolic hypertension in senescence-accelerated mice P1 (SAMP1). The proposed studies are significant as they will reveal, for the first time, an important role of klotho deficiency in the pathogenesis of arterial stiffening. These studies will also demonstrate that arterial stiffening could be an important etiological factor in the development of systolic hypertension. Completion of the project may provide new insights into the therapeutic strategies for the control of arterial stiffening and related cardiovascular complications.